1. Field of the Invention
The present invention concerns a methacrylimide containing polymer of excellent transparency and heat resistance.
2. Description of the Prior Art
Methyl methacrylate polymers are excellent not only in transparency but also in mechanical property and weather proofness and, accordingly, they have been used as high performance optical plastic materials and decorative materials. In recent years, their uses have been developed in the field of short distance light communication or optical sensors.
However, since the heat distortion temperature of methyl methacrylate polymers is not sufficient being as low as about 100.degree. C., their use is often restricted and thus, there is a strong demand in the market for improving the heat resistance.
As a method of improving the heat resistance of a methyl methacrylate polymer, there has been proposed, for example, (1) a method of reacting a polymer of acrylic acid, methacrylic acid or an ester thereof with a primary amine, ammonia or a compound of forming a primary amine or ammonia under the presence of a solvent (U.S. Pat. No. 2146209, German Pat. Nos. 1077872 and 1242369), (2) a method of reacting a methyl methacrylate polymer with a primary amine under the presence of water (U.S. Pat. No. 3284425) or (3) a method of reacting an acrylic polymer and ammonia or primary amine in an extruder (U.S. Pat. No. 4246374).
However, in the method (1) described above, since the boiling point of the solvent used is high, it is difficult to completely separate the solvent from the resultant imidized polymer in a commercial scale and, as a result, the imidized polymer obtained is colored to reduce its transparency. In the method (2) described above, since reaction is conducted under the presence of water, methyl methacrylate segments suffer from hydrolysis in the case of intending to obtain a partially imidized polymer, making it difficult to obtain an imidized polymer having a desired heat resistance, as well as it is also difficult to perform uniform imidization reaction. Further, in the method (3) described above, since the imidization reaction is conducted between a polymer of high viscosity and a gaseous imidizing material, it is difficult to conduct a homogenous imidization reaction making it difficult to obtain a homogenously and partially imidized polymer.
Accordingly, although the heat resistance of the imidized polymers obtained by the methods described above is somewhat improved, since the transparency is poor, the molecular weight is substantially reduced or imidization of the polymer is conducted only not homogenously upon commercial production, these methods have not yet been put to practical use at present.
Laid-Open Japanese patent applications Sho 60-210606 and Sho 62-187705 disclose polymethacrylimides with the total light transmission of 93 -94%, but it is difficult to control the imidization ratio with these methods. Although a polymethacrylimide of narrow distribution of imidization ratio can be obtained in a sampling within a short period of time, imidization ratio fractuates during continuous operation over several hours or several tens of hours.
An object of the present invention is to improve the foregoing drawbacks in the prior art and provide a methacylimide containing polymer possessing properties such as excellent optical property, mechanical property, weather proofness and fabricability inherent in methacrylate polymers and excellent in transparency and heat resistance, more in particular, excellent in transparency.